Ultrasonic inspection method and apparatus

ABSTRACT

Testing method and apparatus, incorporating a pair of transducers positioned on opposite sides of a weld seam. The transducers are alternately energized, and signals from the transducers are gated to develop signals representative of defects in various regions of the workpiece under test. Individual references are established for the different regions, and the signals are compared with the associated references. Output signals representing major defects are generated in accordance with various relationships of signals from the different regions of the workpiece.

Inventors: James M. Toth, Euclid; Tyler W.

[451, Feb. 12, 1974 Judd, Chardon, both of Ohio [73] Assignee:

Republic Steel Corporation,

Cleveland, Ohio Filed:

Aug. 1, 1969 Appl. No.: 846,819

Primary Examiner-Richard C. Queisser Assistant ExaminerJohn P. BeauchampAttorney, Agent, or Firm-Cooper, Dunham, Clark,

Griffin and Moran ABSTRACT Testing method and apparatus, incorporating apair of transducers positioned on opposite sides of a weld seam. Thetransducers are alternately energized, and signals from the transducersare g a t e i tqglevelop sig- [52] US. Cl. 73/67.9 nals representativeof defects in various regions otl the [51] Int. Cl. G0ln 29/04 workpieceunder test. Individual references are estab- [58] Field of Search73/67.5-67.9 lished for the different regions, and the signals arecompared with the associated references. Output sig- [56] ReferencesCited nals representing major defects are generated in ac- UNITED STATESPATENTS cordance with various relationships of signals from the3,221,544 12/1965 Gunkel 73/67.8 different regions of the workpiece3,237,446 3/1966 Wood 73/67.9 3,262,123 7/1966 Crouch 73/67.8 X3,478,308 11/1969 Stanley et a1.. 73/67.7 X 10 Claims 9 Drawing Figures3,481,186 12/1969 Cellitti et a1... 73/679 3,512,399 5/1970 Weinbaum73/675 M0 M54 #1 4 -:l ,4 1 l I A. 6141-5; ure Aft/1*! L- PM TKAPEflaZ,NI/ I I W l l f i I war/50a #05". 4 h em 32 #2 ar Her/1C vui /4 f -1x1)l W255 LOU/7' COZ/F'L/A/G IND/C470,?

l i ,l/HD 4/?5/ LOG/C 22m a GENE/90mg Z2 Z4 L24 PATENTEUFEE 12 m4 sum 5BF 7 ULTRASONIC INSPECTION METHOD AND APPARATUS BACKGROUND AND BRIEFDESCRIPTION OF THE INVENTION This invention relates to testing methodsand apparatus. More particularly it relates to the ultrasonic testing ofspecimens, such as welded pipe.

In the testing of welded pipe to determine defectsfit is important to beable to make a determination of the defects encountered before an outputindication is given that a major defect has been encountered. In thepast the ultrasonic analysis of specimens has generally been achievedwith no other criterion for the classification of a defect other thanthe amplitude of a signal reflected by a defect within the specimenunder test. In the present invention signals from different regions of aworkpiece are analyzed and compared with established thresholds forpredetermined relationships before an output indication is generatedindicating the existence of a flaw (a major or rejectable defect). Suchprocedure permits a greater analysis of signals and the betterclassification of defects.

The invention also utilizes a coupling indicator circuit which providesan indication of the coupling taking place between testing transducersand the specimen or workpiece under test. The coupling indication signalis utilized along with the defect signals developed in the analyzing ofinformation.

Brown et al U.S. Pat. No. 3,041,872, issued July 3 1962, disclosesapparatus for the ultrasonic testing of materials utilizing gating forthe inspection of different regions in a workpiece, as well as automaticgain control to overcome the effects of poor coupling. This patent isrepresentative of the prior art in which the amplitude of a signal isused to define a fault. Establishing different references for differentregions and the simultaneous utilization of these references, as in thepresent invention, is not suggested.

Gordon et al U.S. Pat. No. 3,050,988, issued Aug. 28 1962, discloses anultrasonic testing arrangement involving ultrasonic transducerspositioned on opposite- Sproule U.S PatTNo. 2,969,671, issued Jan. 31:

1961, is directed to an ultrasonic flaw detector. The location andseverity of a flaw is indicated by the circuitry of the patent. Theamplitude of the echo signal as received from a region is representativeof the severity of the defect. Again, as in the other prior art patents,there is no comparison of defects in various regions with FeB'pEfiVi:mamdmme generatioii of an output flaw signal.

TSfebbins e151; U.S. Pat No. 3,164,007, issued Jan. 1965, is directed tothe ultrasonic inspection of workpieces. This patent utilizes a signalgating technique to classify signals according to different regions ofthe.

workpiece under test. Digital signals of different amplitude aregenerated, based on the different regions! There is iio c oinparison ofdefect signals from different regions with respective thresholds as inthe present invention.

1967, is directed to the identification of bond defects. This patentutilizes an ultrasonic testing procedure in which frequency is variedover a range of frequencies and resonance peaks in a detected signal arenoted. Various relationships between the resonance peaks are utilized toclassify the defects. This comparison technique. however, does notsuggest the comparison of signals from different regions of a workpiecewith respective thresholds for the purpose of defect categorization.

Tlie fisent invention accordingly has for an object the categorizationof defects within a workpiece.

Another object of the invention is to carry out defect analysis througha comparison of signals from different regions ofthe workpiece withrespective thresholds.

These and other objects of the invention are carried out, as notedgenerally above, by classifying ultrasonic signals according to regionin a workpiece and comparing the signals from various regions withrespective thresholds in order to develop information regarding defectswithin the workpiece.

W BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram ofatesting system in accordance with the invention, showing a portion of aworkpiece under test.

FIG. 2 is a block diagram of a couplin indicator circuit useful in thesystem of FIG. 1.

FIG. 3 is a block diagram showing representative further details of acoupling circuit as set forth in FIG. 2.

FIG. 5 is a block diagram of the major portion of a representative weldarea and plate area signal generator useful in the system of FIG. 1.

FIG. 5A is a series of waveform diagrams of representative signalsgenerated by circuits such as shown in FIG. 5.

FIG. 6 is a block diagram of a representative logic unit as shown inFIG. 1.

FIGS. 7 and 8 are block diagrams of representative signal analyzersuseful in the system of FIG. 6.

' DETAILED DESCRIPTION FIG. 1

FIG. 1 shows a representative system in-accordance with the invention. Apipe 10 is shown against which are positioned two ultrasonictransducers, designated transducer No. l and transducer No. 2. Thetransducers are utilized for the testing of weld seam I2, typicallyconsisting of a seam portion 12a on the outside of the ,pipe and a seamportion 12b on the inside of the pipe. Each of the transducers may becomposed of one or more transducer elements positioned within a housingand ultrasonically coupled to the pipe 10 by a liquid filrn from asource (not shown). Transducer No. l injects signals into the pipe whichare useful in testing two areas of the pipe. The first area isdesignated weld area No. l and includes the major portion of the weldseam that is closest to that transducer as well as a minor portion ofthe pipe adjacent to the main body of the weld seam. The second area isdesignated plate area No. 1 and is an area of the pipe commencing fromthe edge of weld area No. l closest to transducer No. 1 for a distancetypically chosen so that plate area No. 1 and weld area No. l encompassthe same amount of pipe. The limits of weld area No. l and plate areaNo. l are delineated by gating techniques as will be set forth in moredetail below.

Transducer No. 2 is similarly positioned on the other side of the weldseam 12 for the purpose of testing weld area No. 2 and plate area No. 2corresponding to the weld and plate areas tested by transducer No. 1. Itwill be noted that there is an area of overlap, designated overlap area,in FIG. 1, representing the common portion of the weld seam 12 that istested by both the transducers.

The transducers are coupled by conductors 14 and 16 to a pulsegenerating and gating unit 18. This unit generates pulse signals whichare applied to the transducers to activate the transducers which in turnintroduce pulse signals into the pipe 10. Signals are received by eachof the transducers both by through transmis;

11 from one transducer to t he ot lfrf f by reflection or eaobf a signalfrom one transducer back to that same tfarTsdiiceri'Tliesethrough andecho signals are traiisTnitted by the transducers l and 2 via conductorsl4 and 16 to a coupling indicator 20 and a weld area andiplate areasignal generator 22.

The coupling indicator 20 utilizes a :thmughtransmi i als.{rem9 1s.tradsesttqt so he projyide an ihdicationof the co up lingbetween the twotransducers and the pip el lfi i.e., the qualityT ofthe transmission ofultrasonic signals from one of the transducers through the liquid filmcoupling that transducer to the pipe and finally through the filmcoupling the other transducer to the pipe and ending at the othertransducer. Signals representative of the quality of coupling areapplied by the coupling indicator 20 to a logic unit 24 for utilizationin the analysis of defects in the pipe 10. The coupling indicator 20carries out the analysis of the quality of coupling between transducersand pipe while the testing of the pipe is achieved through echo signalreception by the transducers.

A weld area and plate area signal generator 22 is a signal system underthe control of the pulse generator and gating unit 18. The signalgenerator 22 gates the signals received from the transducers No. l andNo. 2 so that the signals may be classified according to the differentregions of the workpiece under inspection. In FIG. 1 these four regionsare the weld areas No. l and No. 2 and the plate areas No. l and No. 2.Echo signals as classified according to workpiece region are applied tologic unit 24 which compares these signals with preestablishedreferences. Typically the references differ for the various regions ofthe workpiece, which aids in the classification of defects. The logicunit establishes criteria which must be satisfied before a defectrecognized in a certain region is classified as a rejectable flaw.

The logic unit 24 is coupled to an output block 26 representing anysuitable form of output of the system. Typically the block 26 includesvisual indication of I flaws.

FIG. 2.

FIG. 2 is a block diagram ofa representative coupling indicator circuit20 useful in the system of FIG. 1. The system is established to analyzethe through transmission of signals from transducer No. 2 to transducerNo. 1. Signals from the ultrasonic transducer No. 2 are applied to apulse delay and shaping network 28 which generates an output pulse thatis applied to analog gate 30. The pulse from the unit 28 is a gatecontrol pulse that occurs at the time that the through signal fromtransducer No. 2 is expected at transducer No. 1. Accordingly the analoggate receives a signal from the ultrasonic transducer No. 1 aftersuitable amplification and shaping by a unit 32. The analog signal fromthe unit 32 is passed through the analog gate 30 during the gatinginterval and is applied to an integrator or averager 34. The averagersmooths out temporary fluctuations in the signal from the analog gate 30and generates an output signal at an output 36. The amplitude of thesignal at the output 36 is representative of the quality of couplingbetween the transducers and the workpiece. ln particular, as thecoupling becomes poorer, the amplitude of the signal at the outputterminal 36 decreases.

As noted, the averaging smooths out the signal from the analog gate sothat temporary signal fluctuations are discounted. Without suchaveraging, temporary signal fluctuations would have an adverse effect onany system utilizing the coupling signal.

FIG. 3

FlG. 3 shows the details of a circuit as set forth in FIG. 2. The pulsedelay and shaping unit 28 is formed of an amplifier 38 which amplifiesthe signal from ultrasonic transducer No.2. The signal applied to theamplifier 38 is the main pulsing signal that energizes transducer No. 2.The amplified pulsing signal is shaped by a shaping network 40 which maybe of resistancecapacitance-diode configuration. The signal from theshaping network 40 is applied to a screen coupled phantastron delaycircuit 42. This circuit is of conventional construction as described inPulse and Digital Circuits, Millman and Taub, Section 7-7 (McGraw- HillBook Company, Inc., 1956). The delay circuit 42 produces an outputpulse, the trailing edge of which is displaced in time from the inputpulse signal. The time delay is adjusted by varying the voltage at theplate of the tube comprising the phantastron. Typically the plate isclamped to a variable potential source by a diode.

The output from the screen coupled phantastron (typically taken from thescreen grid of the tube) is applied to a shaping network 44 which may bea resistance-capacitance-diode network which shapes the trailing edge ofthe pulse from the phantastron circuit 42. The signal from the shapingnetwork 44 is applied to another screen coupled phantastron circuit 46,typically of fixed delay. In practice the phantastrons 42 and 46 areadjusted so that the phantastron 46 generates an output pulse theleading edge of which occurs slightly before the time that thethrough-transmitted signal from transducer No. 2 reaches transducer No.1 and terminates shortly thereafter. The output pulse from thephantastron 46 is applied as the gating control pulse to an analog gate48 (corresponding to gate 30 in FIG. 2). This analog gate receives itsanalog input from the signal amplification and shaping network 32connected to the ultrasonic transducer No. 1.

The network 32 is comprised of tuned cascaded amplifiers 50, tuned tothe carrier frequency of the ultrasonic signal from transducer No. l.The gain of the amplifier section is typically variable. The signal fromthe amplifier 50 is applied to a half-wave detector 52 which passesone-half of the input signal (of appropriate polarity) which is thenapplied to a filter 54 which may be capacitive and inductive. The filter54 removes the carrier frequency. The signal from the filter 54 is thuscomprised ofa series of unidirectional pulses which are applied to theanalog gate 48. As noted above, the gating control pulse from thephantastron circuit 46 occurs just before and after the time duringwhich the through-transmitted signal from transducer No. 2 is expectedat transducer No. 1. Thus the analog gate 48 passes only that pulsesignal that is through-transmitted from transducer No. 2.

The signal from the analog gate 48 is applied to a pedestal removercircuit 56 which may be formed from a diode clamp which removes thepedestal from the output signal of the analog gate. The pedestal is arectangular pulse of fixed height upon which the desired pulsing issuperimposed. The output pulses from the pedestal remover 56 are appliedto the integrator 34 shown also in FIG. 2. The integrator may comprise adiode and capacitance-resistance network.

The signal from the integrator has an amplitude which varies inaccordance with the amplitude of the pulse signals applied thereto. Theeffect of the integrator is to smooth out any variations in the inputsignal so that the circuit is not subject to temporary fluctuations ininput signal.

The signal from the integrator 34 is applied to a cathode follower 58.The signal from the cathode follower is applied to the output 36 shownalso in FIG. 2. The amplitude of the signal at the output 36 representsthe degree of coupling. As the quality of coupling lessens, the signalat the terminal 36 decreases in amplitude. A strip chart recorder 60 maybe coupled to the terminal 36 to provide a continuous indication of thequality of coupling between the two transducers and the workpiece.

The signal from the integrator 34 is also applied to a voltage divider62 typically resistive and capacitive.

The voltage divider also receives a feedback signal from the cathodefollower 58 applied through a meter 64. The meter 64 provides a visualindication ol the degree of coupling. The signal from the voltagedivider 62 is applied to a Schmitt trigger 66. The Schmitt triggergenerates two levels of output signal based on the relationship of theinput signal applied thereto to a predetermined threshold level. Thethreshold level for the Schmitt trigger represents a predetermineddegree of coupling between transducers. If that coupling is notachieved, the Schmitt trigger controls a relay network 68 so that a notest (coupling lost) indicator 70 is activated which in turn mayactivate an alarm 72. If the predetermined coupling level is achieved,however, the relay network causes a test indicator 74 (coupling good) tobe activated which in turn may activate an event marker 76.

It should be noted that the feedback between the output of cathodefollower 58 and the voltage divider 62 is a form of boot-strapping whichincreases the sensitivity of the Schmitt circuit to variations in thesignal from the integrator 34.

FIG. 4

FIG. 4 shows the details of a representative pulse generating and gatingunit 18 of FIG. I and a representative part of the weld area and platearea signal generator 22 of FIG. 2. A clock pulse generator generates aseries of time-spaced pulses applied to pulse generators 82 and 84.These pulse generators in turn are coupled by conductors 86 and 88 totransducer No. 1 and transducer No. 2 to provide pulse signals whichaltermetransduggg The conductors 86 and 88 coupling together the pulsegenerators and transducers form trigger inputs of a bistablemultivibrator 90. The bistable multivibrator generates outputs onconductors 92 and 94 connected respectively to differentiator andamplifier units 96 and 98. The outputs of the differentiator andamplifier units appear at terminals 100 and 102 (designated trigger No.1 and trigger No. 2). 1

The operation of the bistable multivibrator and the differentiator andamplifier units is as follows: Concurrently with the activationoftransducer No. 1 by the pulse generator 232, the energizing signal onconductor 86 triggers the bistable multivibrator to one stable mode ofoperation in which conductor 92 is active. The differentiator andamplifier unit 96 produces an output pulse at the terminal concurrentlywith the activation of transducer No. 1.

When the transducer No. 2 is activated by a pulse signal on conductor88, that signal triggers the bistable multivibrator 90 to its secondstable condition in which output conductor 9 is active. The renderingactive of that conductor results in a pulse signal at terminal 182 bythe differentiator and amplifier unit 98.

Typically the pulse signals trigger No. i and trigger No. 2 areconcurrent with the leading edges of the pulse signals generated by thepulse generators 82 and 84, i.e., the signals trigger No. l and triggerNo. 2 are generated concurrently with the activation of transducers No.1 and No.2.

The conductors 36 and 88 in FIG. 4 are also applied as analog inputs togated amplifiers I04 aNd 196. The gating inputs to these amplifiers,determining the times during which the amplifiers pass signals, are theoutput conductors 92 and 94 from the bistable multivibrator 90. Each ofthe amplifiers is thus gated ON for a time commencing with theactivation of the associated transducer No. l or No. 2 and remains onuntil the activation of the other transducer. The outputs of the gatedamplifiers 104 and 106 are coupled to an amplifier and processor 108(typically including RF amplification, detection and pulseamplification) which generates output signals at an output terminal I10designated all pulses. The signal at the output terminal Ill) isrepresentative of all pulses either applied to the transducers No. 1 andNo. 2 to activate these transducers or as generated by the transducersupon the receipt of signals by the transducers from the specimen undertest.

FIG. 5

The signals trigger No. 1, trigger No. 2 and all pulses generated at theoutput terminals I90. 192 and 110 of FIG. 4 are utilized in the systemof FIG. 5. FIG. 5 shows a major portion of a representative weld areaand plate area signal generator 22 of FIG. 1. The circuit of FIG. 5 isspecifically intended to generate output signals at terminals 112 and114 representing signals from the transducers No. l and No. 2 and fordifferent regions of the workpiece under test. In particular, there aretwo circuits such as shown in FIG. 5 for developing signals from thefour regions designated weld area No. 1 and weld area No. 2 (onecircuit), plate area No. 1 and plate area No. 2 (other circuit) inFIG. 1. The classification of signals by region within the workpiece isaccomplished by time gating in the circuit of FIG. 5, as will now beexplained.

In FIG. 5 the all pulses signal at terminal 110 is applied as the analoginput to two analog gates 116 and 118. The analog gates transmit theapplied signal from the terminal 110 only when they are activated bygating signals applied thereto from digital gates 120 and 122. Thedigital gates in turn receive signals from a bistable multivibrator 124which has two output conductors 126 and 128. The output conductor 126 isrendered active, enabling the digital gate 120 at the time trigger No. 1appears at terminal 100. As noted above, the signal trigger No. 1 isgenerated concurrently with the leading edge of the signal activatingtransducer No. 1. Similarly output conductor 128 of the bistablemultivibrator 124 is rendered active when the bistable multivibrator hasbeen triggered to its second stable state by the signal trigger No.2appearing at terminal 102. Thus the digital gate 122 has an input signalapplied thereto commencing from the time that the transducer No. 2 isactivated.

The signal trigger N0. 1 and trigger No. 2 are also coupled by an ORgate 130 to a one-shot multivibrator 132. The multivibrator 132, whichmay be of adjustable delay, generates an output pulse signal onconductor 134 that commences a predetermined period of time after themultivibrator has been energized by one of the pulses from the OR gate130. This pulse is applied to another one-shot multivibrator 136 whichgenerates a pulse signal that serves as the gate control of digitalgates 120 and 122. The multivibrator 136 may be made with an adjustabledelay as is the multivibrator 132.

The signal from the multivibrator 132 is chosen to commence apredetermined time after the activation pulse applied to each transducerNo. l and No. 2 in FIG. 1. This determines the time that each of thedigital gates 120 and 122 is first opened. The time during which thegate remains open is determined by the multivibrator 136. Thus it isnoted that the digital gates 120 and 122 are enabled by the gate controlsignals from .multivibrator 136 in turn to enable the analog gates 116and 118 for predetermined periods, each period commencing after theactivation of the corresponding one of transducers No. 1 and No. 2 andpersisting for LELE I'FIQLQE HLEQEIIERELQF As noted above, there is acircuit such as shown in FIG. 5 for each of the two groups of areasshown in FIG. 1 (one group is the two weld areas and the other group isthe two plate areas). The adjustable delay features in themultivibrators 132 and 136 determine the times that each circuit isactive. In particular, one set of delay periods is chosen so that in onecircuit the signals at the terminals 112 and 114 from the two analoggates are representative of signals from weld areas No. 1 and N0. 2. Inthe other circuit the delay periods are chosen so that thesignafi'r'ranfihe'ihaiog gates are from the plate areas No. 1 and No. 2.

By suitable variation of the delay periods, various regions of thespecimen under test can be interrogated. In FIG. 1 weld areas No. 1 andNo. 2 include an area of overlap. It may be desirable to render bothweld areas completely overlapping; alternatively it may be desirable toinclude no overlap in certain circumstances. By the same token, theplate areas may be varied so that they need not abut the correspondingweld areas but rather commence at points displaced from the edges of theweld areas. The definitions ofthe Zones in the workpiece that are underinterrogation may be varied in accordance with the requirements andcharacteristics of a particular workpiece under test. Because of thevariations that may be desirable, it may also be desirable to divide thecircuit of FIG. 5 into two component units each having its own separateone-shot multivibrators 132 and 136 rather than the common units shownin FIG. 5. In this fashion. the gating periods may be changed completelyso that the two weld areas, for example, bear no relation to oneanother.

FIG. 5A

FIG. 5A includes a series of waveform diagrams of representative signalsgenerated by the circuit of FIG. 5. The two uppermost waveformsrepresent the signals trigger No. 1 and trigger No. 2 appearing atterminals and 102 in FIG. 5. A representative time spacing of 0.50milliseconds between trigger signals is indi cated.

In FIG. SA the identification numbers to the left of each waveformcorrespond to the numbers in FIG. 5 adjacent various output conductorsand indicate at what point in FIG. 5 each signal occurs.

The first group of ten waveforms beneath the trigger No. 1 and triggerNo. 2 waveforms shows representative signals from the differentcomponents of FIG. 5 when the circuit of FIG. 5 serves to developsignals from the plate areas associated with transducers No. 1 and No.2. The lowermost group of the waveforms are those obtained when thecircuit of FIG. 5 serves to develop signals from the weld areasassociated with the two transducers.

The following should be noted:

a. 11 is the time which determines the location of each plate area fortransducers No. 1 and No. 2.

b. 22 represents the width of each plate area for transducers No. 1 andNo. 2.

c. :3 is the time which determines the location of each weld area fortransducers No. 1 and No. 2.

d. :4 represents the width of each weld area for transducers No. 1 andNo. 2.

Representative defect signals have been shown in FIG. 5A.

FIG. 6

The circuit of FIG. 6 utilizes the various weld area and plate areasignals, a coupling indication signal and trigger signals in order todevelop information regard ing various defects as detected in differentregions of the workpiece under test. Terminals 112a and 114a,respectively, receive signals from a circuit such as shown in FIG. 5representative of signals within weld areas No. 1 and No. 2. Terminals112b and 114b receive signals from another circuit such as shown in FIG.5 representative of signals within the plate areas Not land N o. 2.Terminal 140 receives a coupling indication signal such as from thecircuit of FIG. 3, in particular, from the no test block 70 of FIG. 3.Thus the signal at the terminal 140 is active when coupling has 9 beenlost, i.e., the degree of coupling has fallen below a predeterminedquality of coupling. The remaining two inputs to the circuit of FIG. 6are trigger No. 1 and trigger No. 2 at terminals 100 and 102 from thecircuit of FIG. 4.

The circuit of FIG. 6 carries out a signal analysis and comparison. Inparticular, signals from each of the regions under test, namely, the twoweld areas and the two plate areas, are analyzed and compared withthresholds and output signals are developed rep r esentative of thecomparisons if various criteria are met. The following discussion willbe helpful to an un derstanding of the circuit of FIGv 6.

Some defects in welded pipe, for example, are as follows: non-fusion (inthe central area .of a weld bead) and slag inclusions, which can occurnear the edges of a weld bead, both of which may be elongated. Otherdefects are gas pockets, edge breaks or cracks, laminations in the plate(planar discontinuities occurring near the edges of the plate), pinholes(gas pockets at the surface of a workpiece) and nonmetallic inclusionssuch as dirt and the like which appear to migrate to the edge of a plateduring the rolling process. The non-metallic inclusions, in particular,may remain along the edges of a plate, even if the plate has beentrimmed along its edges, especially if trimming is not sufficient. Suchinclusions are deleterious when the edges of the plate are abutted andthen welded together, for example, in the fabrication of welded pipe.

It has been found desirable to establish the following conditions forthe generation of flaw signals:

1. Signals from either weld area No. l or No. 2 exceed some preset levelP;

2. Signals from either weld area exceed some lower reject level R for atime greater than T seconds;

3. Signals from either weld area are greater than the reject level R andit has been determined that the quality of coupling between transducersand workpiece has fallen below some predetermined level;

4. Signals from both weld areas are greater than the reject level R;provided that in any of the above conditions I to 4, the signals fromthe plate area on the same side of the weld are less than the rejectlevel R;

5. Signals from a plate area are greater than a predetermined thresholdlevel TH.

In the above conditions a preset level P, a reject level R, a time T,and a threshold level TH have been mentioned. Typically the levels P, Rand TH are related to the signal that is generated when ultrasonicsignals encounter a standard defect. For example, a is inch diameterhole may be drilled through a weld bead in order to constitute astandard defect. Full scale deflection in a meter or on an oscilloscopefrom signals encountering this defect may be considered to correspond tothe threshold level TH. The reject level R may represent one-third fullscale deflection and the preset level P may represent some level withinthe region from onethird to full scale deflection. These indications ofsignal level are illustrative.

In the satisfying of condition 1 above, namely, that either weld areaproduces signals greater than some preset level P, it is considered thata defect has been noted which is sufficiently severe to justify thegeneration of an output flaw signal. The proviso that signals from theplate area on the same side of the weld are less than the reject level Rcompensates for the condition in which a lamination in a plate areagives a false indication of a defect in the weld area.

Condition 2 above, namely, that the signal from either weld area isgreater than the lower reject level R for a time greater than T seconds,proceeds on the assumption that lesser defects than those of condition Iwill be tolerated unless they persist for a time greater than T seconds,which may be related to the length of a flaw. In particular. if pipe isbeing moved past a pair of testing transducers that test the weld beadtherebetween, the time T is related to def ect length by the speed ofmovement of the pipe. As in condition I, the plate area signal from thesame side of the weld must be less than the reject level R in order foran output indication to be given in order to compensate for falseindications of defects in the weld area caused by laminations in theplate area.

In condition 3 an output indication is provided in the event that eitherweld area produces signals that are greater than the lower reject levelR and coupling is indicated as being below the predetermined qualitylevel desired for good operation. In effect this condition compensatesfor the poor coupling, inasmuch as with proper coupling the signal wouldbe greater than the reject levelR. Again in this condition thecompensation for laminations in the plate area is provided.

In condition 4 the criterion is that both weld areas provide signalsgreater than the lower reject level R.

In accordance with the weld area regions shown in FIG. I, both weldareas simultaneously providing signals greater than the reject level R,represent either one defect in the central area of the weld (the overlaparea in FIG. 1) or two defects, each in one of the side portions ornon-common portions of the weld areas. For example, a defect could bepresent in the non-common portion of weld area No. 2 to the right of theoverlap area, and another defect could be present inthe noncommonportion of weld area No. l to the left of the overlap area. In anyevent, these conditions will all re sult in signals in both weld areas.However, it is consid ered that the likelihood of two defectssimultaneously occurring in the two non'common portions of the weldareas is sufficiently unlikely so as to warrant the test criterionspecified. In most cases the presence of signals from both weld areasgreater than the reject level indicates a flaw in the overlap area ofthe weld.

It is to be noted then that defects in the overlap area of the weld areconsidered more serious than defects in the edges of the weld, since thelower reject level R is the signal criterion for defects in this area,while other criteria must be satisfied in the edge areas, namely, thetime T or a higher level P. Again, as in the other conditions noted,compensation for laminations in the plate area is provided. Theestablishing of a more strict standard for the overlap area or centralarea of the weld is emphasized when it is noted that signals from theoverlap area are generally stronger than signals from the edge areas ofthe weld. If the threshold level for detect classification were the samefor all areas, threshold level for the central area would becorrespondingly lower b ecause of the presence of stronger signals. Justthe opposite is achieved by establishing a lower defect classificationlevel in the central area.

Finally. in condition 5. if signals in either plate area exceed arelatively high threshold level TH, an output indication will be given.

The above conditions are reduced in tabular form in Table l, as follows:

Coupling indicator outputs Output I OutputJ Output K 1... Less than 11..Greater than'll-L vv ..c Greater than Rfltlreuter than It"... reaterthan TII ..1 (jood Lost.

"IABL' l Weld urea outputs Plate area outputs Output A Output B OutputOutput 1) Output l) Output F Output G Output 11 Weld area No. Greaterthan l ..e Greater than It or Greater than router than time greater than'1. Less than R Less than Ii.... s 1 Less than R 4 A. .4 Greater than 1...4..... Greater than It for time greater than '1. 0...... Less than IL....4.1.. .t... Less than It 1.... Less than IL. Less than It.

Plate area No.

Weld area No.

Plate area No. 2. C0upling.

In Table l outputs A and B correspond to condition I. Outputs C and Dcorrespond to condition 2. Outputs E and F correspond to condition 3;output G corresponds to condition 4; outputs H and l correspond tocondition 5. Two coupling indicator outputs .I and K have been providedrepresentative of good or poor coupling and are provided by the circuitof FIG. 3, the coupling indicator blocks and 74.

Referring again to FIG. 6, the circuit shown in the figure instrumentsthe logic of Table 1. To this end four signal analyzers 142, 144, 146and 148 are employed receiving signals from circuits such as shown inFIG. 5

and respectively representing signals from weld area No. 1, plate areaNo. 1, weld area No. 2 and plate area No. 2. Representative forms of thesignal analyzers are shown in FIGS. 7 and 8, to be described later. Eachsignal analyzer compares the signals applied thereto against variousreferences and generates output signals representative of thecomparisons.

Signal analyzer 142 takes weld area No. l signals and generates anoutput on conductor 150 if a preset level P is exceeded. A signal isgenerated on an output conductor 152 if the signals from weld area No. 1exceed reject level R for a time greater than T seconds. An outputsignal is generated on conductor 154 if the signals from the weld areaNo. 1 exceed the reject level R.

In similar fashion. signal analyzer 144 generates output signals onconductors 156 and 158 when signals from plate area No. 1 arerespectively less than reject level R and greater than threshold levelTH.

Signal analyzer 146 generates signals similar to those generated bysignal analyzer I42 on output conductors 160, 162 and 164 in connectionwith signals received from weld area No. 2. Signal analyzer 148 issimilar to analyzer 144 and generates output signals on conductors I66and 168 when the signals from plate area No. 2 are respectively lessthan reject level R and greater than threshold level TH.

Considering outputs A and B ofTable 1 corresponding to condition 1above. output A is traced as follows: the signal from weld area No. 1must be greater than preset level P. If this is the case, conductor 150is energized. The signal passes through OR gate 170 energizing one inputof AND gate 172. The other input to the AND gate is received fromconductor 156, which is energized if reject level R is not exceeded inplate area No. l. The output of AND gate 172 is thus energized,energizing OR gate 174. The output of the OR gate appears on conductor176, which is coupled to an AND gate 178. The other input of the ANDgate is received from an OR gate which is in turn connected to terminals100 and 102 receiving triggers No. 1 and No. 2. These trigger signalsare generated, as noted above in connection with FIG. 4, during thetimes that the two transducers are pulsed. Thus the AND gate isenergized by the OR gate 180 for the duration of each trigger pulse.

The AND gate 178 is coupled to a monostable multivibrator 182 whichgenerates an output pulse that activates a weld area marking unit 184 toprovide an indication of a defect in the weld area, in this case outputA of Table 1 above.

Tracing through output B, the cnergization of conductor 160 from signalanalyzer 146 and conductor 166 from signal analyzer 148 causes theenergization of AND gate 186 (the signal from conductor 160 is appliedto the AND gate through OR gate 188). The AND gate 186 energizes the ORgate 174, as noted signal analyzer 148. Energization of these twoconductors leads to the enabling of AND gate 186, leading to theactivation of weld area marking unit 184, as explained above.

In connection with output E of Table l. the signals from weld area No. 1must be greater than the reject level R. When this is the case,conductor 154 from signal analyzer 142 is energized. The signals fromplate area No. 1 must be less than the reject level R. resulting inconductor 156 from signal analyzer 144 being energized. Energization ofthe two conductors 154 and 156 enables AND gate 190, the output of whichis applied through an OR gate 192 to an AND gate 194. The other input tothe AND gate is received from terminal 140, and is active when couplingis lost. Thus AND gate 194 is energized when all of the conditions setforth under output E of Table l have been satisfied. The OR gate 174 isenergized leading to the activation of the weld area marking unit 184.Output F from Table I is similar to output E, the conditions beingsatisfied for weld area No. 2 and plate area No. 2 along with a loss ofcoupling. Output conductor 164 from signal analyzer 146 is energized, asis output conductor 166 from signal analyzer 148. An AND gate 196 isenabled, providing an input to AND gate 194 through OR gate 192. Theother input to the AND gate 194 is energized by the loss of couplingsignal from terminal 140, as de scribed above.

Output G of Table l is traced in the circuit of FIG. 6 as follows:Signals from weld area No. 1 greater than the reject level R causeconductor 154 from signal analyzer 142 to be energized. Signals fromplate area No. 1 less than the reject level R cause conductor 156 to beenergized. AND gate 190 is thereby enabled, the output of which iscoupled to an AND gate 198. Similarly signals from weld area No. 2greater than reject level R cause output conductor 164 from signalanalyzer 146 to be energized. Signals from plate area No. 2 less thanthe reject level R cause conductor 166 from signal analyzer 148 to beenergized. AND gate 196 is thereby en-- abled, the output of which isalso applied to AND gate.

198. The energization of AND gate 198 causes the output conductor 176from OR gate 174 to be energized, leading to the activation of weld areamarking unit 184.

Outputs H and I are the plate area outputs and are active whenever theplate area signals are greater than a threshold level TH. Tracing outputH, the signals from plate area No. 1 are determined to be greater thanthe threshold level TH; thus output conductor 158 from signal analyzer144 is energized. This output conductor is connected to an AND gate 200which receives as its other input the signal trigger No. 1 from terminal100. The signal trigger No. l is active during the time that transducerNo. 1 is pulsed. Thus the AND gate 200 is energized when the plate areaNo. 1 signals are greater than the threshold level'TH, causing amonostable multivibrator 202 to be activated. This multivibratorenergizes a plate area No. 1 marking unit 204 to provide a suitablemarking ofthe plate indicating a defect in plate area No. 1.

Similarly output l of Table l is in connection with signals from platearea No. 2 being detected as greater than a threshold level TH. Outputconductor 168 from signal analyzer 148 is energized under this conditionand energizes one input of AND gate 206. The other input of the AND gateis energized by the signal trigger No. 2 from terminal 102. The AND gate206 energizes monostable multivibrator 208 which in turn activates platearea No. 2 marking unit designated 210 in FIG. 6. Accordingly majordefects in plate area No. 2 result in the suitable marking ofthe platearea by the marking UI'III.

The .remaining two outputs I and K of Table I are coupling indicatoroutputs. These outputs are not shown in FIG. 6 but rather are part ofthe circuit of FIG. 3. Output .1, for example, may be derived from testblock 74 in FIG..3 indicating satisfactory coupling. while output K maybe derived from the no test or coupling lost block in FIG. 3.

FIG. 7

FIG. 7 is a block diagram of a representative weld area signal analyzeruseful in the system of FIG. 6. The circuit shown in FIG. 7 mayinstrument either of the weld area signal analyzers 142 and 146. A weldarea signal is received at terminal 212 corresponding to terminal 1120or 114a in FIG. 6. A gain control unit 214 varies the amplitude of thesignal as desired and supplies output signals to a pulse stretcher 216and a threshold device 217, such as a Schmitt trigger. The pulsestretcher 216 provides a DC output signal generally of varying amplitudethat is proportional to the amplitude ofthe input pulse signal. Theoutput signal from the pulse stretcher is much longer in duration thanthe input signal. For example, the input pulse signal may be 10microseconds in duration, while the output-signal may be l0 millisecondsin duration. The signal from the pulse stretcher 216 is applied to acomparator 218 which is set to a predetermined reference. typicallyvariable in accordance with different defect levels. In any event, thecomparator 218 generates an output signal at terminal 220 ifthe inputsignal exceeds the reference. In the context of the system of FIG. 6,the comparator 218 generates an output signal at the terminal 220 if theinput signal exceeds the preset level P. The terminal 220 corresponds tothe output conductor or from the signal analyzer 142 or 146.

The threshold device 217 provides a digital output signal whenever theinput signalexceeds a predetermined threshold. The threshold in thiscase, again which is generally variable to account for differentfactors, corresponds to the reject level R in the system of FIG. 6. Ifthe reject level is exceeded. the Schmitt trigger generates an outputsignal which is applied via a pulse stretcher 219 to a ramp generator222 and an amplifier-follower 224. The amplifier-follower gener ates anoutput signal at terminal 226 (corresponding to conductor 154 fromsignal analyzer 142 or conductor 164 from signal analyzer 146). Thissignal is active whenever the reject level is exceeded by the weld areasignal.

The ramp generator 222 generates a time varying signal which isinitiated at the time of the digital output signal from the Schmitttrigger 217. The signal from the ramp generator is applied to acomparator 228 which compares the ramp signal with a predeterminedreference representing the time T in the system of FIG. 6. When thesignal from the ramp generator exceeds the reference, an output signalis generated at terminal 230 corresponding to conductor 152 or 162 inFIG. 6. The signal at the terminal 230 indicates that the reject level Rhas been exceeded for a time greater than T, indicating that a defecthas persisted for a given length of time in the weld area as detected byone of the transducers.

FIG. 8

HO. 8 is a block diagram of a representative plate area signal analyzerinstrumenting either of the signal analyzers 144 or 148 of FIG. 6. Aplate area signal is applied to terminal 232. Thisterminal correspondsto terminal ll2b orl14b of FIG. 6. The plate area signal is applied totwo gain control units-234 and 236 which adjust the amplitude of-thesignal. Each of these units is connected inturn to a threshold device orSchmitt trigger 238 or 240. The Schmitt triggers in turn are coupledthrough amplifiers 242 and 244 to terminals 246 and 248. The Schmitttrigger 238 is set to provide an output signal wheneverthe input platearea signal is above a predetermined reference level representing thethreshold level TH. The Schmitt trigger 240 generates an output signalwhenever the input plate area signal falls below a predeterminedreference representing the reject level R in the system of FIG. 6. Thesereferences are generally variable to accommodate different testconditions. i i

What is claimed is: a

l. A method of testing a metallic article that includes a weld seamtherein for flaws, comprising:

a. introducing signals into the article;

b. detecting signals from the article and characterizing them as from afirgt region that includes a portion of the weld seam and a secon dregion of the article adjacent to the weFYse ain? c. establishingindividual thresholds for the first and second regions;

d. comparing the detected signals from the different regions with theassociated established thresholds and e. generating an output flawsignal for the first region when the first region detected signalexceeds its threshold indicating an anomaly in the article and thesecond region detected signal is less than its threshold indicating theabsence of a lamination in the second region.

2. A method according to claim 1, in which the established thresholdsfor said two regions are different.

3. A method according to claim 1, including generating said output flawsignal when the detected signal from the first region exceeds athreshold R for at least a'time T, and the detected signal from thesecond region is less than the threshold R.

4. A method according to claim 1, including characterizing signals alsoas from a third region of the article that includes another portion ofthe weld seam and a fourth region of the article adjacent to the weldseam on the side opposite from the second region, and generating anoutput flaw signal when the detected signals from the first and thirdregions are each greater than a threshold R and the detected signalsfrom the second and fourth regions are each less than the threshold R.

5. Apparatus for testing a metallic article that includes 'a weld seamtherein for flaws, comprising:

a. means for introducing signals into the article;

b. means for detecting signals from the article and characterizing themas from a first region that includes a portion of the weld seam and asecond region of the article adjacent to the weld seam;

c. means for establishing individual thresholds for the first and secondregions;

d. means for comparing the detected signals from the two regions withthe associated established thresholds and r e. means responsive to themeans (d) for generating an output flaw signal for the first region whenthe first region detected signal exceeds its threshold indicating ananomaly in the article and the second region detected signal is lessthan its threshold indicating the absence ofa lamination in the secondregion.

6. Apparatus according to claim 5. in which the means (c) includes meansfor establishing different thresholds for the two article regions.

7. Apparatus according to claim 5, in which the means (e) includes meansfor generating said output flaw signal when the detected signal from thefirst region exceeds a threshold R for at least a time T, and thedetected signal from the second region is less than the threshold R.

8. Apparatus according to claim 5, in which the means (b) includes meansfor characterizing the detected signals from the article as from a thirdregion that includes another portion of the weld seam and a fourthregion of the article adjacent to the weld seam on the side oppositefrom the second region, and the means (e) includes means for generatingan output flaw signal when the detected signals from the first and thirdregions are each greater than a threshold R and the detected signalsfrom the second and fourth regions are each less than the threshold R.

9. A method according to claim 1, in which the signals that areintroduced into the article are ultrasonic.

10. Apparatus according to claim 5, in which the means (a) comprisesmeans for introducing ultrasonic signals into the article.

8 k =k l

1. A method of testing a metallic article that includes a weld seamtherein for flaws, comprising: a. introducing signals into the article;b. detecting signals from the article and characterizing them as from afirst region that includes a portion of the weld seam and a secondregion of the article adjacent to the weld seam; c. establishingindividual thresholds for the first and second regions; d. comparing thedetected signals from the different regions with the associatedestablished thresholds and e. generating an output flaw signal for thefirst region when the first region detected signal exceeds its thresholdindicating an anomaly in the article and the second region detectedsignal is less than its threshold indicating the absence of a laminationin the second region.
 2. A method according to claim 1, in which theestablished thresholds for said two regions are different.
 3. A methodaccording to claim 1, including generating said output flaw signal whenthe detected signal from the first region exceeds a threshold R for atleast a time T, and the detected signal from the second region is lessthan the threshold R.
 4. A method according to claim 1, includingcharacterizing signals also as from a third region of the article thatincludes another portion of the weld seam and a fourth region of thearticle adjacent to the weld seam on the side opposite from the secondregion, and generating an output flaw signal when the detected signalsfrom the first and third regions are each greater than a threshold R andthe detected signals from the second and fourth regions are each lessthan the threshold R.
 5. Apparatus for testing a metallic article thatincludes a weld seam therein for flaws, comprising: a. means forintroducing signals into the article; b. means for detecting signalsfrom the article and characterizing them as from a first region thatincludes a portion of the weld seam and a second region of the articleadjacent to the weld seam; c. means for establishing individualthresholds for the first and second regions; d. means for comparing thedetected signals from the two regions with the associated establishedthresholds and e. means responsive to the means (d) for generating anoutput flaw signal for the first region when the first region detectedsignal exceeds its threshold indicating an anomaly in the article andthe second region detected signal is less than its threshold indicatingthe absence of a lamination in the second region.
 6. Apparatus accordingto claim 5, in which the means (c) includes means for establishingdifferent thresholds for the two article regions.
 7. Apparatus accordingto claim 5, in which the means (e) includes means for generating saidoutput flaw signal when the detected signal from the first regionexceeds a threshold R for at least a time T, and the detected signalfrom the second region is less than the threshold R.
 8. Apparatusaccording to claim 5, in which the means (b) includes means forcharacterizing the detected signals from the article as from a thirdregion that includes another portion of the weld seam and a fourthregion of the article adjacent to the weld seam on the side oppositefrom the second region, and the means (e) includes means for generatingan output flaw signal when the detected signals from the first and thirdregions are each greater than a threshold R and the detected signalsfrom the second and fourth regions are each less thAn the threshold R.9. A method according to claim 1, in which the signals that areintroduced into the article are ultrasonic.
 10. Apparatus according toclaim 5, in which the means (a) comprises means for introducingultrasonic signals into the article.